Fincher, E. B.
Abelard-Schuman, 1955
Buku Teks
New York United Nations 1989,
Buku Teks
Risjord, Norman K.
Prentice-Hall, 1985
Buku Teks
Rand McNally and Company.
Rand Mcnally & Company, 2006
Buku Teks
Washington U.S. Department of Health, Education, and Welfare 1955
Buku Teks